Use Case 13: passing options with resource sets

This use case extends Use Case 12: it is suggested to try it before this one.

Prepare a sample shell script

Create a simple shell script inside your /tmp directory (or whereever you prefer): it’s a sample script that accept two options:

tiian@mojan:/tmp$ cat print_and_wait.sh 
#!/bin/sh
echo "First arg is $1 (sleep time), second arg is $2 (assigned resource)"
echo "Sleeping $1 seconds"
sleep $1
echo "Releasing resource $2"
tiian@mojan:/tmp$

Use your preferred editor to prepare the above script and name it “print_and_wait.sh”

Don’t forget to attribute exec bits to the shell command

tiian@mojan:/tmp$ chmod 755 print_and_wait.sh 
tiian@mojan:/tmp$ ls -la print_and_wait.sh 
-rwxr-xr-x 1 tiian tiian 150 2014-05-05 22:30 print_and_wait.sh
tiian@mojan:/tmp$

execute it directly to test it’s working as expected:

tiian@mojan:/tmp$ ./print_and_wait.sh 2 foo
First arg is 2 (sleep time), second arg is foo (assigned resource)
Sleeping 2 seconds
Releasing resource foo
tiian@mojan:/tmp$

if all above is OK, we are ready to use it with flom.

Open four terminals and try this experiment:

1. switch every terminal to /tmp directory with command “cd /tmp”
2. inside every terminal write this command at prompt, but do not press “enter”: “flom -o 0 -r red.green.blue -- ./print_and_wait.sh 3”
3. now press “enter” key at the first terminal
4. switch to second terminal and press “enter” key
5. switch to third terminal and press “enter” key
6. switch to fourth terminal and press “enter” key

Expected result:

1. the script execution inside the first terminal acquires the resource “red” (the first resource in the set)
2. the script execution inside the second terminal acquires the resource “green” (the second resource in the set)
3. the script execution inside the third terminal acquires the resource “blue” (the third resource in the set)
4. the script execution inside the fourth terminal does not start because there is no an available resource and flom command specifies ‘-o 0’ (no wait) option.

Terminal 1 output:

tiian@mojan:/tmp$ flom -o 0 -r red.green.blue -- ./print_and_wait.sh 3
First arg is 3 (sleep time), second arg is red (assigned resource)
Sleeping 3 seconds
Releasing resource red
tiian@mojan:/tmp$

Terminal 2 output:

tiian@mojan:/tmp$ flom -o 0 -r red.green.blue -- ./print_and_wait.sh 3
First arg is 3 (sleep time), second arg is green (assigned resource)
Sleeping 3 seconds
Releasing resource green
tiian@mojan:/tmp$

Terminal 3 output:

tiian@mojan:/tmp$ flom -o 0 -r red.green.blue -- ./print_and_wait.sh 3
First arg is 3 (sleep time), second arg is blue (assigned resource)
Sleeping 3 seconds
Releasing resource blue
tiian@mojan:/tmp$

Terminal 4 output:

tiian@mojan:/tmp$ flom -o 0 -r red.green.blue -- ./print_and_wait.sh 3
Resource already locked, the lock cannot be obtained
tiian@mojan:/tmp$

Explanation:

the first command “flom -o 0 -r red.green.blue -- ./print_and_wait.sh 3” locks the first resource in the set, the second command flom -o 0 -r red.green.blue -- echo locks the second resource in the set, the third command flom -o 0 -r red.green.blue -- echo locks the third resource in the set, but the fourth command can not lock a resource: it should wait but it can’t due to “-o 0” option (no wait behavior).
From terminal (1-3) outputs you can understand the resource name is passed as the last command line option to the flom managed command (“print_and_wait.sh” script in the above example).

Summary

This use case explains you how the assigned resource name is passed to the command managed by flom.

See also

FLoM available arguments are documented in man page: use man flom. FLoM configuration explains how you can specify flom behavior without using command line arguments.